OSPF Router Type

By dividing the OSPF network into areas, the OSPF routers contained in each area and the routers connecting between areas can be classified as follows

  • Internal Router
  • Backbone router
  • Area Border Router : ABR
  • Autonomous System Boundary Router : ASBR

Internal Router

A router in which all interfaces belong to the same area is called an internal router. A router whose all interfaces belong to the backbone area is both a backbone router and an internal router.

Backbone router

A router that has at least one interface that belongs to a backbone area is called a backbone router. Area border routers are also backbone routers, as they connect the backbone area to other areas.

Area Border Router : ABR

A router that has interfaces that belong to multiple areas and interconnects the areas is called an area border router (ABR). ABR has a link state database for each area, and exchanges link state information for each area. Each area must, in principle, be adjacent to the backbone area, which means that the ABR maintains separate link-state databases for the backbone area and for the other areas. The ABR is also both an exit and an entrance to an area. The ABR plays a very important role in the advertisement of OSPF route information and the actual packet forwarding.

In addition, ABR can perform route summary.

Autonomous System Boundary Router : ASBR

Autonomous System Boundary Routers (ASBRs) are routers located at the boundary between a network that performs routing with OSPF (OSPF domain) and a network that performs non-OSPF routing such as static routes, RIP/EIGRP/BGP (non-OSPF domain).

ASBRs are routers that are configured to redistribute from non-OSPF routing processes to OSPF. Note that since the communication is bi-directional, the ASBR also needs to redistribute OSPF routes to non-OSPF domains.

Related article

The following article explains more about redistribution.

Figure OSPF Router Type
Figure OSPF Router Type

Related articles

How the OSPF works